This project is an investigation of the dynamic movements which phospholipids and cholesterol can undergo in the membranes of mammalian cells, and the results which perturbations in the spatial distribution of these components can have on cellular activity. Special attention is given to the possible role which lipids and cholesterol may play in the control of abnormal cell growth and differentiation. To test the interrelation between membrane dynamics and biological functions of cells, information about the spatial distribution of cell surface lipids and cholesterol will first be obtained. A variety of normal and transformed tissue culture cell lines will be radioactively labeled with specific lipid components, and the distribution of these components determined by high resolution EM autoradiography and cell fractionation techniques. Special attention will be focused on the possible compositional asymmetry of the plasma membrane lipids and cholesterol. The exchange of phospholipids between contiguous cells in culture will also be investigated since this process represents a unique kind of intercellular communication, which may be responsible for alterations of cell lipids in vivo. The molecular exchange of phospholipids between contacting cells, will be studied autoradiographically, and biochemially using a specially designed filter technique which will permit complete separation of donor and recipient cells. While the consequences of variations in the phospholipid and cholesterol content of mammalian cell membranes are unknown, it is reasonable to assume that such variations might have a profound effect on the physiology of the cell. In order to better delineate this problem, the effects of cell surface lipid and cholesterol modifications on lymphocyte activation by mitogens such as Concanavalin A, and on DNA synthesis in a synchronized population of Chinese hamster fibroblasts will be investigated.